The present invention relates generally to a transponder apparatus for receiving and re-transmitting pulsed RF signals, and more specifically, a tunable transponder apparatus that provides for the retransmission of a received signal, while minimizing interference and/or clock jitter associated with prior art transponders.
Radar identification systems have been known for many years, having originated during the Second World War. In such systems, an interrogation apparatus sends out a radio frequency pulse, which is recognized by an identification apparatus fitted to a vehicle or other object within range of the interrogation apparatus.
Upon receipt of the pulse, a repeater sends back a reply signal, generally in the form of a train of pulses, which is processed and displayed at a receiving station. Such systems, which require the provision of a responder on the vehicle or other object, are known as secondary radars, or repeaters, as distinct from primary radars which work by passive reflection of radio waves by targets. Normally, a repeater operates in conjunction with a primary radar so that the responses received from repeaters on radar targets can be correlated/identified from the echoes received by the primary radar from the targets themselves. FIG. 5 illustrates an exemplary prior art repeater system. The repeater system of FIG. 5 includes a receiver 504 for receiving the radar pulse, a filter 502 for filtering out noise, and an amplifier 506 for amplifying the signal and for re-transmitting the signal (repeating).
As radar systems become more sophisticated, and more sensitive, repeater systems have also become more complex. However, these complex repeater systems are prone to interference, stemming, in part, from feedback of the retransmitted signal generated by the repeater. Further, these repeater systems lack the ability to provide adequate isolation between input and output to provide sufficient power at low input signal levels.
Transponders overcome the foregoing power problem associated with simple repeater systems. FIG. 6 illustrates an exemplary prior art transponder system. As illustrated in FIG. 6, the transponder includes an input antenna 601, a receiver 604 for receiving the radar pulse, a filter 602 for filtering out noise, a second signal source generator 606 for generating a new carrier signal, logic circuitry 608 for re-clocking the received signal to the new carrier signal, and an amplifier 610 for amplifying the filtered signal, and an output antenna 609 for retransmitting the signal (transponding). In a transponder, the received signal is detected and is re-clocked with the new carrier signal prior to amplification and transmission.
Radar related systems have been further used to detect signals from uncooperative sources or emitters and to track such signals. Typically, these systems utilize pulse-repetition-interval (PRI) trackers. As explained in detail below, a PRI tracker is an apparatus that synchronizes with a received pulse train associated with a given signal and a generates an output signal corresponding to the expected PRI of the incoming signal.
Notwithstanding the foregoing use of repeater and transponder systems, as stated such prior art systems are prone to interference and lack the ability to provide adequate isolation between input and output to produce sufficient power at low input signal levels. Furthermore, prior art radar transponders add unacceptable clock jitter to the retransmitted signal for certain applications. Still further, the retransmitted signal from the transponder is additionally subject to interference resulting from the feedback.
It is an object of this invention to provide a transponder that corrects the foregoing deficiencies in the prior art systems.
More specifically, it is an object of the present invention to provide a transponder that minimizes its vulnerability to interference.
It is another object of this invention to provide a transponder that is able to provide sufficient power at low input levels.
It is an object of the present invention to eliminate clock-jitter from a re-transmitted signal. In other words, the present invention allows for an accurate and consistent reproduction of the leading edge of the return signal, thereby allowing for the elimination of interference caused by random and/or improperly generated return signals.
The present invention provides a method of transponding pulsed RF signals comprising the steps of receiving pulsed RF signals having a plurality of PRIs, generating, with a PRI tracker, control signals from the received pulsed RF signals, filtering the received pulsed RF signals with the control signals to thereby obtain enable signals, and controlling a transmitter with the enable signals.
In one embodiment of the present invention the step of controlling a transmitter further includes the step of enabling an amplifier, the amplifier receiving an input signal from an input signal generator, and the amplifier outputting an amplified version of the input signal in accordance with the enable signals. Particularly, the amplifier is an RF amplifier and the input signal generator is a tunable RF source. More particularly, the RF amplifier is a traveling wave tube amplifier and the tunable RF source is a synthesizer.
In another embodiment of the present invention the step of filtering the received pulsed RF signals with the control signals to thereby obtain enable signals further includes, inputting the received pulsed RF signals from the receiver into one input of a logic AND gate, and inputting the control signals from the PRI tracker into the other input of a logic AND gate.
The present invention further provides a method of transponding pulsed RF signals comprising the steps of, receiving a plurality of pulsed RF signals, each pulsed RF signal having a plurality of PRIs, selecting, with a PRI tracker, one pulsed RF signal out of the plurality of pulsed RF signals, generating, with a PRI tracker, a control signal from the selected pulsed RF signal, filtering the selected pulsed RF signal with the control signal to thereby obtain an enable signal, and controlling a transmitter with the enable signal.
The present invention still further provides a pulsed RF signal transponder comprising a receiver for receiving pulsed RF signals having a plurality of PRIs, a PRI tracker for generating control signals from the received pulsed RF signals, an enable signal generator for receiving the received pulsed RF signals and the control signals as input, and for generating enable signals as output, and a transmitter, controlled with the enable signals, for transmitting.
In one embodiment of the present invention the transmitter further includes, an amplifier; and an input signal generator, wherein the amplifier, after receiving an input signal from the input signal generator, outputs an amplified version of the input signal in accordance with the enable signals. Particularly, the amplifier is an RF amplifier and the input signal generator is a tunable RF source. More particularly, the RF amplifier is a traveling wave tube amplifier and the tunable RF source is a synthesizer.
In another embodiment of the present invention, the enable signal generator further includes a logic AND gate.
The present invention still yet further provides a pulsed RF signal transponder comprising a receiver for receiving a plurality of pulsed RF signals, each pulsed RF signal having a plurality of PRIs, a PRI tracker for selecting one pulsed RF signal out of the plurality of pulsed RF signals, and for generating a control signal from the selected pulsed RF signal, a filter for filtering the selected pulsed RF signal with the control signal to thereby obtain an enable signal, and a transmitter.
In one embodiment of the present invention, the transmitter further comprises an amplifier, the amplifier receiving an input signal from an input signal generator, and the amplifier outputting an amplified version of the input signal in accordance with the enable signal. Particularly, the amplifier is an RF amplifier and the input signal generator is a tunable RF source. More particularly, the RF amplifier is a traveling wave tube amplifier and the tunable RF source is a synthesizer.
In one embodiment of the present invention, the filter further includes a logic AND gate.
The transponder of the present invention provides important advantages over the prior art devices. Most importantly, it allows for the accurate and consistent reproduction of the leading edge of the return signal, thereby allowing for the elimination of interference caused by random and/or improperly generated return signals that can be improperly construed by the radar system as the return pulse of the transponder.
Additional advantages of the present invention will become apparent to those skilled in the art from the following detailed description of exemplary embodiments of the present invention. The invention itself, together with further objects and advantages, can be better understood by reference to the following detailed description and the accompanying drawings.